1. Field of the Invention
The invention relates to spectrophotometers and, more particularly, to spectrophotometers operating under control of a programmable processor.
2. Prior Art
Spectrophotometers are commonly used in the measurement of color for compliance with a predetermined standard for quality-control purposes. Such measurements are commonly made on products such as fabrics, photographs, and the like, typically using permanently installed equipment. Color measurements must also be made on automobiles and other larger bodies or structures, and for such purposes, portable spectrophotometers may be used.
The measurement of color involves measuring light reflected from an object and determining the intensity of its color components. Photodetectors are used to convert optical signals to electrical signals which are indicative of the intensity of the optical signal. The generated electrical signals are used to compute spectral values which are compared against a standard to determine whether the color of an object meets the standard for that object.
Spectrophotometers typically include a source of light projected onto an object, photodetectors detecting light reflected from the object, and signal processing circuitry connected to the photodetectors to compute curves or numerical values indicative of color. The general principles of color measurement and the construction of use of color measuring instruments are well known and understood by those skilled in the art and are described in published texts such as the Measurement of Appearance, by Richard S. Hunter, John Wiley & Sons, 1975, and the Measurement of Colour, by William D. Wright, Van Nostrand, Reinhold Co., 1969.
Different types of spectrophotometers are known using angular or spherical optical measuring devices for the measurement of color in different circumstances. State-of-the-art spectrophotometers, whether using angular or spherical optical devices, include microprocessors which perform some signal processing on the electrical signals generated by the photodetectors in order to compute numerical values indicative of color. Such microprocessors may be programmed to execute a variety of algorithms, not only for the basic computation of data reflective of the measured color, but also for comparing the resultant data with data indicative of upper and lower limits of a color standard in order to provide a pass/fail test. State-of-the-art spectrophotometers may also provide an audible signal or an electronically displayed message to an operator indicating the results of a pass/fail test.
Known spectrophotometers may also display text in the form of specific instructions to an operator regarding the use or calibration of the device.
A problem with the prior art devices is that they are specifically designed for a particular job or operation and are not readily adaptable to accommodate changes in quality-control procedures which are required from time to time. Furthermore, each company or organization generally has its own requirements for quality control and consequently for color measurements. Even though portable spectrophotometers typically include a programmable microprocessor, its programs are not readily alterable since, for cost, space and reliability reasons, the programs are embedded in firmware, such as integrated circuit read-only memory devices. In the prior art, the introduction of a change in the program sequences which define color computations to be performed by the microprocessor requires the generation of a new, firmware imbedded program by the manufacturer and replacement or modification of the read-only memory. Furthermore, each company, or in larger companies, each operational department, has different specific requirements which are desirable to be programmed into the spectrophotometer. Accordingly, there tends to be a proliferation of spectrophotometers, all of which must be separately produced or modified by the manufacturer.
A significant concern by companies using spectrophotometers is the delay which is necessarily introduced between the time that the need for a new spectrophotometer is recognized and the time that such a device is shipped and ready for use. A further shortcoming of known spectrophotometers is that the operator has to be provided with separate instructions as to what measurements are to be taken, the order in which they are to be taken, etc. Such instructions are usually in the form of a paper document with specific steps to be followed and requiring the operator to make written notations identifying the measurements recorded in the instrument.